178 Onpure Caoutchouc. [1826. 



charcoal and compounds of carbon and hydrogen ; it yields no 

 ammonia by destructive distillation, nor any compounds of 

 oxygen, and my experiments agree with those of Dr. Ure, in 

 indicating carbon and hydrogen as its only elements. I have 

 not, however, been able to verify his proportions, which are 90 

 carbon, 9*11 hydrogen, or by theory nearly 3 proportionals of 

 carbon to 2 of hydrogen, and have never obtained quite so 

 much as 7 carbon to 1 hydrogen by weight. The mean of my 

 experiments gives, 



Carbon . . 6'812~\ f8 proportionals nearly. 



Hydrogen . 1'OOOJ L7. 



No means which have yet been discovered seem competent, 

 when the caoutchouc has once been aggregated, to restore it to 

 its pristine state. Previous to its aggregation it may be either 

 scented or coloured. A solution of camphor in alcohol was added 

 to water, so as to precipitate the camphor in a flocculent state ; 

 a little of this was added to some of the pure caoutchouc in 

 water well agitated, and then coagulation caused by heat or 

 absorption ; the caoutchouc obtained was highly odorous. 



In the trials made to give it colour, the body colours were 

 found to answer best indigo, cinnabar, chrome-yellow, car- 

 mine, lake, &c., were rubbed very fine with water ; then mixed 

 well with the pure caoutchouc, in a somewhat diluted state, and 

 coagulation induced either upon an absorbent surface or other- 

 wise. Perfectly-coloured specimens were thus obtained. 



The aqueous liquid obtained either by letting the sap stand 

 for some time, or by the first and second washing, was of a 

 brown colour, bitter, acid to litmus in consequence of the pre- 

 sence of acetic acid, due apparently to spontaneous changes in 

 the substances present. It was difficult to filter. Being boiled, 

 acid vapours rose, a precipitate fell to the bottom, and now the 

 solution (a) became clear, either by standing or filtration, and 

 could be separated from the solid matter. 



The precipitate or substance thus obtained was dark brown, 

 glossy and brittle, much heavier than water, not soluble in 

 alcohol, ether, water, essential or fixed oils. Weak solution of 

 alkali dissolved it, forming a deep brown solution, precipitable 

 by dilute muriatic acid. It burnt upon platina-foil, like animal 

 matter, with flame, leaving a bulky charcoal. When heated in 



